Saw The Book of Mormon at the Gammage and it was a blast! By the time we got within a few blocks of the venue, we only had a half hour to spare before start time. After parking, walking, buying a drink and finding our seats, we actually had 10 minutes to spare. In other words, the the staff really had the large crowd covered. The entire stage was visible from Orchestra A (we are of average height).
Why 4 starts versus 5? The bathroom situation; they are Ill-equipped for sold out crowds in terms of the number of facilities. I made it back to my seat with a few seconds to spare during intermission.
Overall, I would definitely go to another show at this venue.
**A suggestion: Take a route that gets you to the Apache Lot (one block away), a route away from the Gammage. Parking was $6. This appeared to save us a lot of time.